1. Field of the Invention
This invention relates to printing and editing systems in general, and more specifically to a method for arranging the memory in an electronic dynamic shift register for performing multiple operations. The shift register memory is arranged with control codes such that input, output, and revision operations can occur during each memory revolution. System control logic is provided which recognizes the control codes and controls the input, output, and revision operations.
2. Description of the Prior Art
The prior art devices include the Magnetic Tape "Selectric"* Typewriter. One of the problems encountered when utilizing a single tape Magnetic Tape "Selectric"* Typewriter is that when a revision is to be made, the revision cannot be more extensive than the original recording or the previously recorded material will be overrun. This problem was alleviated on the MT/ST by providing a second tape and transferring the contents of the original tape to the second tape along with revisions (insertions and deletions) performed during the transfer. 6 *Trademark, International Business Machines Corporation
However, the problem of blank blocks on the tape is still present. Also, during scanning, encountering blank positions requires time for reading or special logic to skip these blank positions. The present invention improves on the MT/ST system in that due to the structure of the dynamic shift register, the data is packed so that no blank spaces in text are present. Further, the sections in the buffer are expandable; allowing for input and deletion while maintaining a packed memory. In addition, the memory cycle is very short, and therefore, the data in the buffer can be readily scanned and a correction of improperly recorded material is easily handled.
Another problem which is still present is the inability to perform overlapped operations. It has not been possible to perform combinations of input, output, and revision operations simultaneously during a memory revolution. This is because of tape handling and addressing problems inherent in a tape system. That is, only that part of the tape being used is subject to any given operation at any one time. For another operation to occur, the operation must be interrupted and another part of the tape addressed.